Field of the Invention
The present invention relates to an engine system having an EGR apparatus. More particularly, the present invention relates to an engine system having an EGR apparatus correctly measuring and controlling a recirculation gas flow rate.
Description of Related Art
An engine of a vehicle combusts a mixture of air inflowing from the outside and a fuel with an appropriate ratio to generate power.
In a process of generating power by driving the engine, the external air for the combustion must be appropriately supplied to obtain a desired output and combustion efficiency. For this, a turbocharger as a device for turbocharging the air for the combustion to increase the combustion efficiency of the engine is used.
In general, a turbocharger is a device that rotates a turbine by using pressure of exhaust gas discharged from an engine and thereby increases output of the engine by supplying high-pressure air to a combustion chamber by using rotational force thereof. The turbocharger is applied to both a diesel engine and a gasoline engine.
Further, a nitrogen oxide (NOx) included in the exhaust gas is regulated as an atmospheric pollution source and there has been an effort to lessen exhaust of NOx.
An exhaust gas recirculation (EGR) system has been provided to a vehicle for reducing noxious exhaust gas. Generally, NOx is increased in a case where an air-fuel ratio of an air-fuel mixture is high, which is necessary for sufficient combustion. Thus, the exhaust gas recirculation system mixes exhaust gas from an engine with the air-fuel mixture, for example at 5-20%, thereby reducing the amount of oxygen in the air-fuel mixture and obstructing combustion, and so lessening generation of NOx.
The exhaust gas recirculation (EGR) system of the gasoline engine is a system mounted to the vehicle for fuel consumption improvement. A pumping loss may be reduced in a low speed/low load situation through the exhaust gas recirculation system and ignition timing may be advanced because of a temperature reduction of a combustion chamber, thereby improving the fuel consumption of the vehicle.
As a representative exhaust gas recirculation system, there is a low pressure exhaust gas recirculation (LP-EGR) device. The LP-EGR device recirculates the exhaust gas passing through a turbine of the turbocharger into an intake pathway of a front stage of a compressor.
The exhaust gas recirculation system according to a conventional art supplies the recirculation gas to the combustion chamber of the engine by a torque of the turbine and the compressor when the turbocharger is operating.
However, when the turbocharger is not operating, since almost no negative pressure is generated at the front stage of the compressor, use of a separate differential pressure generation valve is considered. However, if the differential pressure generation valve is mounted, manufacturing cost of the vehicle is increased.
Also, when a differential pressure sensor detecting a pressure difference between a front stage and a rear stage of the EGR valve controlling the amount of the recirculation gas is mounted, since the pressure difference between the front stage and the rear stage of the EGR valve is small in the low speed/low load region, precision of the EGR control decreases.
Accordingly, since the correct amount of recirculation gas may not be controlled, combustion stability may not be obtained such that the ignition timing may not be advanced and it is difficult to improve the fuel consumption of the vehicle.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.